A device manufacturing method includes projecting a patterned beam of radiation through an optics compartment and a channel that provides an open connection between the optics compartment and a substrate compartment onto a substrate, maintaining an ionized flush gas at a higher pressure in the channel than in the substrate compartment and in the optics compartment during the projecting, intercepting particles that emanate from the substrate with the ionized flush gas, pumping the flush gas carrying the intercepted particles from the substrate compartment using a pump coupled to a gas outlet coupled to at least one of the compartments, and establishing an electrical potential difference between a wall of the channel and the outlet and/or a rotor of the pump so that the outlet and/or the rotor of the pump attracts positively charged ions that stem from the flush gas in the channel.